A loan shark who made £88,000 in interest from a victim's initial borrowings of only £500 left court in a Jaguar today, while another was jailed for five years for threatening and blackmailing more than 1,000 poverty-stricken clients.

Both men were condemned by judges at separate courts in the north of England. Agencies and government ministers warned borrowers to avoid backstreet lenders and seek debt advice.

The extraordinary spiral of repayments demanded by 39-year-old Robert Reynolds, of Stanley, County Durham, was revealed by 40-year-old victim Debra Wilson at Newcastle upon Tyne crown court.

She said Reynolds, who lives nearby, posed as a friend who would want only "a bit of interest" when she borrowed the £500 at Christmas nine years ago to buy a computer as a present for her daughter.

Within days, he told her he was only a go-between for the actual lender, who wanted £250 a month – a lie he maintained for eight years while Wilson and her husband, Kevin, took out more loans in a hopeless attempt to meet interest which grew much faster.

The court heard the Wilsons had remortgaged their home, paid Reynolds most of £4,000 given to Mr Wilson as compensation for a motorbike accident, and had their gas cut off because they could not meet payments.

Mrs Wilson, who has three other children, suffered two strokes and a brain haemorrhage during the eight-year ordeal and blamed it on Reynolds.

Meanwhile, he lavishly furnished his home, buying two flatscreen TVs and other luxuries with the money he was getting from his victims.

Ann Richardson, prosecuting, told the court: "The final straw only came in January 2008 when Mrs Wilson's daughter came home with a bag of food leftovers from her babysitting job, saying she was sick of being hungry.

"There was no gas, the house was freezing, and Mrs Wilson went to the police."

While she was at the police station, Reynolds rang with his weekly demand for more money.

PC Natalie Hulse told the court she had listened in to the call and said its tone was "calm and eerie".

"He told Mrs Wilson that he wanted £1,600 by the end of the month, £585 by the end of the week and £85 that day – and suggested someone else might get nasty if she didn't pay," she said.

Reynolds admitted harassment with intent to commit violence, but told the court he was penniless and registered disabled with arthritis and psoriasis.

He was sentenced to 51 weeks in prison, suspended for two years, by Judge John Evans, who told him: "You are a person without a conscience and you should be stamped with a government health warning as anybody who comes into contact with you will be at risk of damaging their health.

She had been left fearing for her life after a concrete block was flung at her windows and Kiely paid her a threatening visit.

"You put your face so close to hers she thought you were going to headbutt her," the judge said. When Kiely was arrested last October, he had an estimated £800,000 owing in loans and interest. Originally from the travelling community, he invested £800,000 in his seven-bed mansion at Chapel-en-le-Frith.

Speaking after the hearing, Ockerby said Kiely – who has a previous conviction for assault – preyed on people's misfortune.

"There are more like him out there," she added. "People need to be aware. You will never get to the end of the last payment. It just goes on and on and on."

Kevin Brennan, the junior minister for consumer affairs, said a government drive against loan sharks had secured more than 100 prosecutions.

"Thugs like Kiely who prey on vulnerable people cause untold misery within communities," he said.